Maybe its not fecal matter.Is it kind of black looking? sugar water will get moldy after awhile. I don't see how you could get fecal matter in the jar because it works on gravity. maybe you can but i've never seen it

When I have feeded with sugar bees at autumn, sugar liquid get fungus if there is a little bit dirt in the case. Dirt gives necessary nutritients to bacterium or fungus growth and it happens what happens. Pure sugar does not allow the growth.

So, clean very carefully the bottle, all parts an use pure sugar liquid.

Bee can transfer dirt to the feeding case and fungus get a foot step from dirt.